f2fs: fix remount problem of option io_bits

Currently we show mount option "io_bits=%u" as "io_size=%uKB",
it will cause option parsing problem(unrecognized mount option)
in remount.
Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -1330,7 +1330,8 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 				from_kgid_munged(&init_user_ns,
 					F2FS_OPTION(sbi).s_resgid));
 	if (F2FS_IO_SIZE_BITS(sbi))
-		seq_printf(seq, ",io_size=%uKB", F2FS_IO_SIZE_KB(sbi));
+		seq_printf(seq, ",io_bits=%u",
+				F2FS_OPTION(sbi).write_io_size_bits);
 #ifdef CONFIG_F2FS_FAULT_INJECTION
 	if (test_opt(sbi, FAULT_INJECTION)) {
 		seq_printf(seq, ",fault_injection=%u",